Process and combined plant for storage and recovery of energy

ABSTRACT

The present invention relates to a process and plant for storage and recovery of energy using a combined plant that comprises a gas treatment unit and an energy generation unit, wherein in a first operating mode, a low-temperature gas liquefaction product is generated from compressed feed gas that is cooled in a heat-exchange system, and using the gas liquefaction product, a storage liquid is provided, and in a second operating mode, using the stored liquid, a low-temperature process liquid is provided that is warmed in the heat-exchange system, obtaining a pressurized fluid that is work-producingly expanded in the energy generation unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from European Patent Application EP 14004152.6 filed Dec. 9, 2014.

BACKGROUND OF THE INVENTION

The present invention relates to a process and a combined plant for storage and recovery of energy, in particular electrical energy, according to the preambles of the respective independent claims.

For example, DE 31 39 567 A1 and EP 1 989 400 A1 disclose using liquid air or liquid nitrogen, that is to say low-temperature air liquefaction products, for grid control and provision of control capacity in electric power grids.

At cheap electric power times, or times of electric power surplus, in which electric power is available inexpensively, in this case compressed feed air is liquefied in an air separation plant with an integrated liquefier or in a dedicated air liquefaction plant, here generally, as explained below, also termed air treatment unit, in whole or in part to give such a low-temperature air liquefaction product. The low-temperature air liquefaction product is stored as low-temperature stored liquid in a storage system having low-temperature tanks. In the storage system, in addition to the low-temperature air liquefaction product, further low-temperature fluids can also be stored. This operating mode proceeds in a period which here is termed energy storage period.

At peak load times, a low-temperature process liquid is formed from the low-temperature stored liquid, which low-temperature process liquid can likewise also comprise further low-temperature fluids. The low-temperature process liquid is, optionally after pressure elevation by means of a pump, warmed to about ambient temperature or above, and thereby transformed into a gaseous or supercritical state. A pressurized stream obtained in this case is expanded to ambient pressure in an energy production unit in one or more expansion turbines with intermediate warming. The mechanical power released is transformed into electrical energy in one or more generators of the energy production unit and fed into an electric grid. This operating mode proceeds in a period which here is designated energy recovery period.

The cold liberated during the energy recovery period on conversion of the low-temperature process liquid to the gaseous or supercritical state can be stored and used during the energy storage period for providing cold for obtaining the air liquefaction product. Thus, it is known from WO 2014/026738 A2 to cool the compressed feed air used for obtaining the air liquefaction product to two different temperature levels in counterflow to two cooled organic coolants in the energy storage period and, in the energy recovery period, to warm the described low-temperature process liquid against the then warmed coolants, as result of which the coolants are cooled again.

Compressed air storage power plants are also known in which air is not liquefied, but rather is compressed in a compressor and stored in an underground cavern. In times of high electric power demand, the compressed air is passed from the cavern into the combustion chamber of a gas turbine. At the same time, fuel, for example natural gas is fed to the gas turbine via a gas line and burnt in the atmosphere formed by the compressed air. The exhaust gas formed is expanded in the gas turbine, as result of which energy is generated. The present invention is, in addition, to be differentiated from processes and devices in which an oxygen-rich fluid is passed into a gas turbine for supporting oxidation reactions. Corresponding processes and devices operate with air liquefaction products which contain more than 40 mole percent oxygen.

The processes known from the prior art for storing and recovering energy, in particular electrical energy, frequently prove to be insufficiently efficient. In addition, combustible fluids such as hydrocarbons, alcohols, etc., are used here as organic coolants. In the process known from WO 2014/026738 A2, these and the compressed feed air and/or the low-temperature process liquid are each conducted through heat-exchanger passages that are separate from one another of one or more shared counterflow heat exchangers. Since corresponding combustible fluids, however, in the case of leaks, can come into contact with oxygen-containing fluids, complex safety measures are required.

Although it is known in principle from U.S. Pat. No. 6,295,837 B1 to use an inert gas (for example nitrogen or a noble gas such as argon) as coolant in a cold circuit, here, cold is continuously transferred from liquid natural gas via a corresponding cold circuit by means of heat exchangers to a stream to be compressed, and to be cooled in or upstream of an air separation plant, and the natural gas is vaporized in the course thereof. As a result, U.S. Pat. No. 6,295,837 B1, as is also explicitly mentioned there, is specifically tailored to combined processes with integrated gasification (integrated gasification combined cycle, IGCC), where nitrogen and oxygen are continuously required at a high pressure, typically more than 10 bar, and at the same time the vaporized natural gas can be used as secondary fuel for heat recovery. The process proposed in U.S. Pat. No. 6,295,837 B1 is unsuitable for a process for storage and recovery of energy, because it provides only cold transfer in one direction. This also applies to a process which is disclosed in U.S. Pat. No. 3,058,314 A.

Also, US 2014/0245756 A1 discloses cryogenic energy storage systems and also processes for the storage of cold energy and reuse thereof.

The object of the present invention is therefore to provide a process which is efficient and simpler in terms of safety for storage and recovery of energy, for example using an air liquefaction product.

SUMMARY OF THE INVENTION

Against this background, the present invention proposes a process for the storage and recovery of energy and a corresponding combined plant having the features: a process for storage and recovery of energy using a combined plant that comprises a gas treatment unit and an energy generation unit, wherein

-   -   in a first operating mode, a low-temperature gas liquefaction         product is generated from compressed feed gas that is cooled in         a heat-exchange system of the gas treatment unit, and using the         gas liquefaction product, a stored liquid is provided,     -   in a second operating mode, using the stored liquid, a         low-temperature process liquid is provided that is warmed in the         heat-exchange system, obtaining a pressurized fluid that is         work-producingly expanded in the energy generation unit,     -   the compressed feed gas is cooled in a first heat-exchange unit         of the heat-exchange system in the first operating mode in         counterflow to a heat-transfer fluid, and the process liquid is         warmed in the first heat-exchange unit in the second operating         mode in counterflow to the heat-transfer fluid,     -   the heat-transfer fluid is cooled in the first operating mode at         least in part by means of at least two further heat-exchange         units of the heat-exchange system that are operated at different         temperature levels, and also each having at least one organic         coolant, and said heat-transfer fluid is warmed in the second         operating mode,     -   the directions in which the heat-transfer fluid and the feed gas         are conducted through the first heat-exchange unit in the first         operating mode are opposite to the directions in which the         heat-transfer fluid and the process liquid are conducted         therethrough in the second operating mode, and     -   the heat-transfer fluid and the compressed feed gas are         conducted, in the first operating mode, in each case at first         pressure levels, and the heat-transfer fluid and the process         liquid, in the second operating mode, are conducted in each case         at second pressure levels through the first heat-exchange unit,         wherein the first pressure levels are at least 5 bar above the         second pressure levels.

The invention further discloses a combined plant for storage and recovery of energy, having a gas treatment unit and an energy generation unit, wherein the combined plant has means which are equipped

-   -   to generate a low-temperature gas liquefaction product, in a         first operating mode, from compressed feed gas that is cooled in         a heat-exchange system of the gas treatment unit, and using the         gas liquefaction product, to provide a stored liquid,     -   to provide a low-temperature process liquid, using the stored         liquid, in a second operating mode, to warm said low-temperature         process liquid in the heat-exchange system, obtaining a         pressurized fluid, and to work-producingly expand the         pressurized fluid in the energy generation unit,     -   to cool the compressed feed gas in a first heat-exchange unit of         the heat-exchange system in the first operating mode in         counterflow to a heat-transfer fluid, and to warm the process         liquid in the first heat-exchange unit in the second operating         mode in counterflow to the heat-transfer fluid,     -   to cool the heat-transfer fluid in the first operating mode at         least in part by means of at least two further heat-exchange         units of the heat-exchange system that are operated at different         temperatures and also with respectively at least one organic         coolant, and to warm said heat-transfer fluid in the second         operating mode,     -   to set the directions in which the heat-transfer fluid and the         feed gas are conducted through the first heat-exchange unit in         the first operating mode opposite to the directions in which the         heat-transfer fluid and the process liquid are conducted         therethrough in the second operating mode, and     -   to conduct the heat-transfer fluid and the compressed feed gas,         in the first operating mode, in each case at first pressure         levels, and the heat-transfer fluid and the process liquid, in         the second operating mode, in each case at second pressure         levels through the first heat-exchange unit, wherein the first         pressure levels are at least 5 bar above the second pressure         levels.

Preferred embodiments are in each case subject matter of the dependent claims, and also of the following description.

Before the advantages achievable in the context of the present invention are explained, the technical bases thereof and some of the expressions used in this application will be explained in more detail.

An “energy production unit” here is taken to mean a plant or a plant component which is equipped for generating electrical energy. An energy production unit comprises here in the context of the present invention at least one expansion turbine which is advantageously coupled to at least one electrical generator. An expansion machine coupled to at least one electrical generator is customarily also termed “generator turbine”. The mechanical power liberated in the expansion of a pressurized fluid in the at least one expansion turbine or generator turbine can be converted into electrical energy in the energy production unit.

The production of air products in liquid or gaseous state by low-temperature separation of air in air separation plants is known and described, for example, in H.-W. Häring (editors), Industrial Gases Processing, Wiley-VCH, 2006, in particular section 2.2.5, “Cryogenic Rectification”. Air separation plants have distillation column systems which can be designed, for example, as two-column systems, in particular as classical Linde-double column systems, but also as three- or multicolumn systems. In addition to the distillation columns for producing nitrogen and/or oxygen in liquid and/or gaseous state (for example liquid oxygen, LOX, gaseous oxygen, GOX, liquid nitrogen, LIN and/or gaseous nitrogen, GAN), that is to say the distillation columns for nitrogen-oxygen separation, distillation columns for producing further air components, in particular the noble gases krypton, xenon and/or argon, can be provided.

The present invention can comprise the production of an air liquefaction product, using compressed feed air. The plant components used therefor can be summarized under the expression “air treatment unit”. In the language use of the present application, this is taken to mean a plant which is equipped for producing at least one air liquefaction product, using compressed feed air. It is sufficient for an air treatment unit for use in the present invention that a corresponding low-temperature air liquefaction product can thereby be obtained that it usable as stored liquid and is transferable to a storage system. This can be an air separation plant, as described above, but also merely a pure “air liquefaction plant”, which does not have a distillation column system. Furthermore, the structure of an air liquefaction plant can correspond to that of an air separation plant having the delivery of an air liquefaction product. Of course, liquid air can also be generated in an air separation plant as air liquefaction product. Since, according to the invention, a gas other than air can also be used, a corresponding plant here is also more generally termed “gas treatment unit”.

The compressed feed air from which the air liquefaction product is produced in corresponding air-treatment units can be provided in a known main (air) compressor having a booster or any other device equipped for the compression of air, as can also be used in conventional air separation plants. For details, reference may be made to the literature cited with reference to air separation plants.

An “air product” is any product that can be produced at least by compression and cooling of air and in particular, but not necessarily, by a subsequent low-temperature rectification. In particular, it can in this case be a liquid or gaseous oxygen (LOX, GOX), liquid or gaseous nitrogen (LIN, GAN), liquid or gaseous argon (LAR, GAR), liquid or gaseous xenon, liquid or gaseous krypton, liquid or gaseous neon, liquid or gaseous helium etc., but also, for example, liquid air (LAIR). The expressions “oxygen”, “nitrogen” etc. in this case also denote respectively low-temperature liquids or gases that have the respectively cited air component in an amount which is above that of atmospheric air. Therefore, it need not necessarily be pure liquids or gases having high contents. Correspondingly, here, an “air liquefaction product” is taken to mean a corresponding liquid product at low temperature. The same applies also to a “gas product” or “gas liquefaction product” that cannot be produced, or cannot only be produced, from air, but also from another gas.

A “heat exchanger” serves for the indirect transfer of heat between at least two streams, e.g. conducted in counterflow to one another, for example a warm compressed air stream and one or more cold streams, or a low-temperature liquid air product and one or more warm streams. Typically, in the context of the present invention, counterflow heat exchangers are used. A heat exchanger can be formed from a single heat-exchanger section, or a plurality of parallel-linked and/or serially-linked heat exchanger sections, e.g. of one or more plate heat exchanger blocks. In this case this is a plate heat exchanger (plate fin heat exchanger). Such a heat exchanger, for example also the “main heat exchanger” of an air treatment plant, via which the main fraction of the fluids that are to be cooled or warmed are cooled or warmed, respectively, has passages which are constructed as fluid channels that are separate from one another having heat exchange surfaces and are combined in parallel and separated by other passages to form “passage groups”. A “heat-exchange unit” can have one or more heat-exchanger blocks or sections.

The present application uses the expressions “pressure level” and “temperature level” for characterizing pressures and temperatures, whereby it must be stated that corresponding pressures and temperatures in a corresponding plant need not be used in the form of exact pressure or temperature values in order to implement the concept according to the invention. However, such pressures and temperatures are typically in certain ranges which are, for example, ±1%, 5%, 10%, 20% or even 50% about a mean value. Corresponding pressure levels and temperature levels can in this case be in disjoint ranges or in ranges which overlap one another. In particular, for example, pressure levels include unavoidable or expected pressure drops, for example on account of cooling effects. The same applies to temperature levels. The pressure levels stated here in bar are absolute pressures.

The present invention has been described previously and will be described hereinafter with reference to air as a working medium. However, it is also suitable for use with other media that are liquefiable in similar manner, for example nitrogen, oxygen, argon and mixtures of these gases.

The present invention proceeds from a process for storage and recovery of energy using a combined plant that comprises a gas treatment unit and an energy generation unit. As is known in principle, in a corresponding combined plant, in a first operating mode, a low-temperature gas liquefaction product can generated from compressed feed gas that is cooled in a heat-exchange system of the gas treatment unit, and using the gas liquefaction product, a stored liquid can be provided. If the compressed feed gas is compressed feed air, the gas treatment unit is an air treatment unit. However, the invention, as mentioned, is not restricted to the use of air. The stored liquid can be, as already mentioned, for example a corresponding liquid gas. When compressed feed air is used as compressed feed gas, it is, in particular, liquid air and/or any other liquid air product which can be formed from correspondingly compressed feed air.

In addition, such a process comprises providing, in a second operating mode, using the storage liquid, a low-temperature process liquid that is warmed in the heat-exchange system, obtaining a pressurized fluid that is then work-producingly expanded in the energy generation unit, for example in this case a generator turbine. The second operating mode can, for example, follow the first operating mode directly, but also further operating modes can be provided between the first and second operating modes. To this extent the process proposed according to the invention corresponds to the prior art in which a liquid air product is generated from air, stored and later vaporized to form a corresponding pressurized fluid.

If in the context of the present invention, it is mentioned that “using the gas liquefaction product a stored liquid is provided”, this may be taken to mean that the stored liquid need not be formed exclusively from the gas liquefaction product, also, for example external, low-temperature liquefaction products or other streams can be provided, that is to say, for example, can be fed into a corresponding storage system. Correspondingly, the wording that “using the stored liquid a low-temperature process liquid is provided”, is to comprise that the low-temperature process liquid also can be provided using additional, also, for example, external, low-temperature liquefaction products or other streams.

The invention provides the compressed feed gas is cooled in a first heat-exchange unit of the heat-exchange system in the first operating mode in counterflow to a heat-transfer fluid, and the process liquid is warmed in the first heat-exchange unit in the second operating mode in counterflow to the heat-transfer fluid. The use of a heat-transfer fluid in the context of the present invention has the particular advantage that additional organic coolants which, as mentioned, can contain combustible hydrocarbons, are not conducted through the same heat exchanger as the compressed feed gas and/or the process liquid, and therefore, in the event of leaks, cannot come into contact with oxygen which may be present in the compressed feed gas or the process liquid. For this purpose, the heat-transfer fluid used is preferably free from, or low in oxidizing and combustible components, in particular is oxygen-free in the meaning explained hereinafter. The heat-transfer fluid is therefore advantageously generally neither oxidizing nor combustible itself, wherein “oxidizing” is taken to mean a property of a fluid of supporting a combustion even in the absence of atmospheric oxygen, under the conditions prevailing in a corresponding heat exchanger.

In addition, the present invention provides that the heat-transfer fluid is cooled in the first operating mode at least in part by means of at least two further heat-exchange units of the heat-exchange system that are operated at different temperature levels and having in each case at least one organic coolant, and said heat-transfer fluid is warmed in the second operating mode. The operating mode termed here as “first operating mode” is the abovementioned operating mode in the energy storage period that a corresponding combined plant carries out at times of electric current surplus when sufficient favorable electrical energy for compressing gas and providing a gas liquefaction product is available. Correspondingly, the “second operating mode” denotes the operating mode in the energy recovery period, that is to say in phases of electric power deficit, in which a corresponding pressurized fluid is generated, using the gas liquefaction product generated in the first operating mode.

In addition, the invention provides that the directions in which the heat-transfer fluid and the feed gas are conducted through the first heat-exchange unit in the first operating mode are opposite to the directions in which the heat-transfer fluid and the process liquid are conducted through the first heat-exchanger unit in the second operating mode. This permits in each case the temperature profiles, according to which cooling and/or heating of corresponding fluids is performed, to be situated close to one another, because the heat-transfer fluid and the feed gas which flow in counterflow to one another through the first heat-exchange unit, in each case can be conducted therethrough with the lowest possible temperature difference.

The invention further provides that the heat-transfer fluid and the compressed feed gas are conducted, in the first operating mode, in each case at first pressure levels, and the heat-transfer fluid and the process liquid, in the second operating mode, are conducted in each case at second pressure levels through the first heat-exchange unit, wherein the first pressure levels are at least 5 bar above the second pressure levels. In other words, the operating pressures of the heat-transfer fluid are different in the first and second operating modes. For this purpose, a pressure control device can be provided. The pressure of the heat-transfer fluid is guided in this case in each case by the pressure of the feed gas, and/or of the process liquid in the first heat-exchange unit, in such a manner that for this reason also a particularly effective heat transfer is possible.

It is particularly advantageous when the first pressure levels, i.e. the first pressure level at which the heat-transfer fluid is conducted in the first operating mode through the first heat-exchange unit, and the first pressure level at which the compressed feed gas is conducted through the heat-exchange unit in the first operating mode, are roughly the same. This also applies to the second pressure levels, i.e. the second pressure level at which the heat-transfer fluid is conducted through the first heat-exchange unit in the second operating mode, and the second pressure level at which the process liquid is conducted through the first heat-exchange unit in the second operating mode. The pressure levels are “roughly the same”, for example, if they do not differ from one another by more than 20%, in particular by no more than 10%, no more than 5%, or no more than 1%. “Roughly” the same pressure levels also include identical pressure levels. In such “roughly the same” pressure levels, the particularly effective heat transfer mentioned is possible. However, exactly the same pressures need not be used.

The first pressure levels of the first operating mode are advantageously at 50 to 120 bar, and/or the second pressure levels of the second operating mode are advantageously at 40 to 60 bar. As mentioned, the pressure difference is at least 5 bar, the first pressure levels, however, can also be 10, 15, 20, 30, 40, 50, 60, 70 or 80 bar above the second pressure levels.

The present invention therefore provides, in addition to the stored liquid which is provided, using the compressed feed gas, and is stored in the first operating mode, and is vaporized in the second operating mode, providing further cold stored fluids in the form of the organic coolants. The at least two further cold stored fluids, that is to say the organic coolants, are in this case preferably arranged for storage of cold at different temperature levels, therefore have, for example, different boiling points which make them suitable for use at different temperatures. In this manner, the cooling of the compressed feed gas in the first operating mode becomes particularly efficient. The same applies to the warming of the low-temperature process liquid in the second operating mode. Overall, the present invention, owing to the use of in total at least three cold stored fluids, namely the gas liquefaction product formed from the compressed feed gas, with the use of which a stored liquid is provided, and the at least two organic coolants, for example hydrocarbons, permits particularly efficient operation.

As discussed above, advantageously, the heat-transfer fluid used is an oxygen-free or substantially oxygen-free gas mixture. It is self-evident that a correspondingly “oxygen-free” gas mixture can also have residual contents of oxygen, for example 1%, 0.5%, 0.1% or 0.01% oxygen or less. Correspondingly low oxygen contents reduce sufficiently the risk of inflammation on contact with an inflammable organic coolant.

Advantageously, the heat-transfer fluid used is a fluid predominantly containing nitrogen, neon, helium and/or argon. This is suitable, particularly, because it is possible by using a corresponding fluid to establish particularly narrow temperature profiles in the heat exchangers used and to minimize thermodynamic losses. An example thereof is illustrated in the accompanying FIG. 5.

Advantageously, here, the heat-transfer fluid, during cooling of the compressed feed gas, is at least in part vaporized, and on warming the process liquid is at least in part liquefied. The present invention, however, does not explicitly refer to processes in which corresponding heat-transfer fluids are expanded and recompressed in order thereby to generate cold. In the context of the present invention, a corresponding heat-transfer fluid is preferably conducted in a circuit in which a maximum pressure difference of at most 5 bar, in particular at most 1 bar, 0.5 bar, or less, occurs. The production of cold therefore proceeds not with the use of the heat-transfer fluid itself, this serves only for heat transfer, and is therefore not cold-producingly expanded and/or recompressed.

Advantageously, the at least two further heat-exchange units comprise a second heat-exchange unit that is operated with a first organic coolant that is transferred between two storage containers. A corresponding second heat-exchange unit can in this case be equipped for operation at higher temperatures in comparison with a third heat-exchange unit, as is described hereinafter and can be operated with a corresponding organic coolant. This is transferred between the two storage containers, as mentioned, of which one is designed as a “warm” storage container, and one as a “cold” storage container. Corresponding storage containers are preferably constructed as insulated tanks. For cooling the compressed feed gas in the first operating mode, in this case, the first organic coolant is conducted from the “cold” storage container through the second heat-exchange unit, where it cools the heat-transfer fluid, and is then transferred to the “warm” storage container. Correspondingly, a transfer in the reverse direction proceeds during a warming of the low-temperature process liquid in the second operating mode.

In particular, as organic coolants for comparatively high temperatures, halogenated or non-halogenated alkanes or alkenes, alcohols and/or aromatics are suitable, as are known fundamentally. For example, halogenated or non-halogenated alkanes or alkenes such as ethane, ethylene, propane, propylene, butane, pentane, hexane and, optionally, also higher hydrocarbons may be used. Halogenated hydrocarbons are in particular fluorinated and/or chlorinated. In addition, suitable first organic coolants are alcohols such as methanol, ethanol, propanol, butanol, pentanol, hexanol, and further alcohols and aromatics such as, for example, toluene.

As mentioned hereinabove, the at least two further heat-exchange units can advantageously comprise a third heat-exchange unit that, in comparison with the second heat-exchange unit, is operated at a lower temperature, preferably with a second organic coolant that is transferred between two heat-storage containers, and also with a third organic coolant that is transferred between two storage containers. With reference to the explanations and the transfer of corresponding organic coolants, reference is made to the above explanations for the second heat-exchange unit. In particular, the process according to the invention, in an advantageous embodiment, can comprise that the second and the third organic coolants are an identical organic coolant, and so the provision of different coolants can be dispensed with. Advantageously, the second and/or third organic coolant, in the context of the present invention, comprises a halogenated or non-halogenated alkane or alkene having at most four carbon atoms that is suitable for particularly low temperatures.

The organic coolant or coolants (the first, the second and/or the third organic coolant) in this case are, in the context of the present invention, warmed in the first operating mode to in each case the same (“upper”) temperature level, from which they are cooled in the second operating mode. Conversely, it or they are cooled in the second operating mode to the same (“lower”) temperature level, from which they are warmed in the first operating mode. Because of unavoidable losses, here, “the same temperature level” is not to be taken to mean only exactly the same temperature, but a temperature band of a width of up to, for example, 20° C. Of course, a temperature difference as low as possible between the two operating modes should be sought. The heat-exchange diagrams of the heat-exchange system of the gas treatment unit can be made particularly expedient by the heat-exchange units used.

A process is particularly advantageous in which the first organic coolant, i.e. the coolant of the second heat-exchange unit, is warmed in the first operating mode from a lower temperature level at −100 to −30° C., in particular −60 to −40° C., to an upper temperature level at 0 to 80° C., in particular 20 to 50° C., and in the second operating mode is cooled from the upper temperature level to the lower temperature level.

A process is further advantageous, in which the second organic coolant, i.e. one of the coolants of the third heat-exchange unit, is warmed in the first operating mode from a first temperature level at −200 to −140° C., in particular −196 to −150° C., to a second temperature level at −100 to −30° C., in particular −60 to −40° C., and in the second operating mode is cooled from the second temperature level to the first temperature level.

In this embodiment of the process according to the invention, advantageously, the third organic coolant, which is likewise a coolant of the third heat-exchange unit, in the first operating mode is warmed from a third temperature level at −200 to −140° C., in particular −196 to −150° C., to a fourth temperature level at −140 to −60° C., in particular −100 to −60° C., and in the second operating mode is cooled from the fourth temperature level to the third temperature level.

In this case, in the first operating mode, advantageously, the second organic coolant at the first temperature level and the third organic coolant at the third temperature level are fed to the third heat-exchange unit, and the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level are withdrawn therefrom. Correspondingly, advantageously, in the second operating mode, the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level are fed to the third heat-exchange unit and the second organic coolant at the first temperature level and the third organic coolant at the third temperature level are withdrawn therefrom.

A corresponding combined plant is advantageously constructed for carrying out a corresponding process. The second organic coolant in this case is advantageously conducted through the third heat-exchange unit completely, the third organic coolant, only in a section thereof. As also explained with reference to the accompanying FIG. 5, particularly favorable temperature courses result therefrom in the first heat-exchange unit.

The organic coolants used differ in their chemical composition, in particular in their boiling point. They must be selected in such a manner that they are liquid in the respective entire working range. In addition to the abovementioned organic coolants, the substances listed in the table on page 5 of WO 2014/026738 A2 come explicitly into consideration for use in the invention as first, second and/or third organic coolant.

Organic coolants can also be the following coolants according to the familiar DuPont nomenclature (cf. DIN 8960, section 6.3.2), namely halogenated and non-halogenated hydrocarbons having one carbon atom such as R-10, R-11, R-12, R-12B1, R-12B2, R-13, R-13B1, R-14, R-20, R-21, R-22, R-22B1, R-23, R-30, R-31, R-32, R-40, R-41 and R-50, having 2 carbon atoms such as R-110, R-111, R-112, R-112a, R-113, R-113a, R-114, R-114a, R-115, R-116, R-120, R-122, R-123, R-123a, R-123b, R-124, R-124a, R-125, R-131, R-132, R-133a, R-134, R-134a, R-141, R-141b, R-142, R-142b, R-143, R-143a, R-150, R-150a, R-151, R-152a, R-160 and R-170, having two carbon atoms and C double bond such as R-1112a, R-1113, R-1114, R-1120, R-1130, R-1132a, R-1140, R-1141 and R-1150, having 3 carbon atoms such as R-211, R-212, R-213, R-214, R-215, R-216, R-216ca, R-217, R-217ba, R-218, R-221, R-222, R-222c, R-223, R-223ca, R-223cb, R-224, R-224ca, R-224cb, R-224cc, R-225, R-225aa, R-225ba, R-225bb, R-225ca, R-225cb, R-225cc, R-225da, R-225ea, R-225eb, R-226, R-226ba, R-226ca, R-226cb, R-226da, R-226ea, R-227ea, R-236fa, R-245cb, R-245fa, R-261, R-261ba, R-262, R-262ca, R-262fa, R-262fb, R-263, R-271, R-271b, R-271d, R-271fb, R-272, R-281 and R-290, having 3 carbon atoms and C double bond such as R-1216, R, R-1225ye, R-1225zc, R-1234ye(E), R-1234ye(Z), R-1234yf, R-1234ze, R-1243zf and R-1270, fluorinated hydrocarbons having 4 or more carbon atoms such as R-C316, R-C317 and R-C318, chlorine-free and fluorine-free hydrocarbons having 4 or more carbon atoms such as R No., R-600, R-600a, R-601, R-601a, R-601b, R-610, R-611, R-630 and R-631, zeotropic mixtures of corresponding coolants such as R401A, R-401B, R-401C, R-402A, R-402B, R-403A, R-403B, R-404A, R-405A, R-406A, R-407A, R-407B, R-407C, R-407D, R-408A, R-409A, R-409B, R-410A, R-410B, R-411A, R-411B, R-412A, R-413A, R-417A, R-422A, R-422B, R-422C and R-422D, and also azeotropic mixtures of corresponding coolants such as R-500, R-501, R-502, R-503, R-504, R-505, R-506, R-507[A], R-508[A], R-508B and R-509[A].

In the context of the present invention, advantageously, a fourth heat-exchange unit can be used, by means of which the heat-transfer fluid is in part cooled in the first operating mode and which is operated with a further compressed feed gas that is cold-producingly expanded. In this manner, in particular, in the first operating mode, additionally cold can be generated to cover cold losses, as is also known in air separation plants, in this case in the form of what is termed a turbine stream.

The present invention also extends to a combined plant for storage and recovery of energy which has all the means that make it suitable for carrying out a process described above. With regard to features and advantages of a corresponding combined plant, reference is made explicitly to the corresponding claim and the above explanations.

In particular, in a corresponding combined plant, a third heat-exchange unit is constructed in such a manner that, in the first operating mode, the second organic coolant at the first temperature level and the third organic coolant at the third temperature level can be fed to said third heat-exchange unit, and the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level can be withdrawn therefrom, and, further, in the second operating mode, the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level can be fed to said third heat-exchange unit, and the second organic coolant at the first temperature level and the third organic coolant at the third temperature level can be withdrawn therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and preferred embodiments of the invention are described in more detail with reference to the accompanying drawings.

FIG. 1A illustrates a combined plant according to an embodiment of the invention in a first operating mode in the form of a process flow diagram.

FIG. 1B illustrates the combined plant according to FIG. 1A in a second operating mode in the form of a process flow diagram.

FIG. 2A illustrates components of a heat-exchange system according to an embodiment of the invention in the first operating mode in the form of a process flow diagram.

FIG. 2B illustrates the components according to FIG. 2A in the second operating mode in the form of a process flow diagram.

FIG. 3A illustrates components of a heat-exchange system according to an embodiment of the invention in the first operating mode in the form of a process flow diagram.

FIG. 3B illustrates the components according to FIG. 3A in the second operating mode in the form of a process flow diagram.

FIG. 4A illustrates a combined plant according to a further embodiment of the invention in the first operating mode in the form of a process flow diagram.

FIG. 4B illustrates the combined plant according to FIG. 4A in the second operating mode in the form of a process flow diagram.

FIG. 5 illustrates heat-exchange profiles achievable according to an embodiment of the invention in a diagram.

In the figures, elements and fluid streams corresponding to one another are illustrated with identical reference signs. In all of the figures, plants and/or plant components are illustrated in various operating modes, which in addition to the elements shown have additional elements such as valves and fittings. Corresponding valves and fittings, for the sake of clarity, are not illustrated, but for explanation, fluid pathways that are blocked by valves and fittings, and/or correspondingly inactivated streams, are drawn criss-crossed. Streams present predominantly or exclusively in gaseous form are illustrated in the form of non-filled (white) arrow triangles, predominantly or exclusively liquid streams are illustrated in the form of filled (black) arrow triangles. The invention is illustrated with reference to an air treatment unit as gas treatment unit.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A illustrates a combined plant according to an embodiment of the invention in a first operating mode in the form of a process flow diagram. The combined plant which is illustrated in FIG. 1B in a second operating mode is designated overall 100, and comprises an air treatment unit 110 and an energy generation unit 120.

In the air treatment unit 110, in the example shown, feed air in the form of a stream a is taken in by suction via a filter 1 by means of a main air compressor 2 having intercoolers that are not drawn separately. The feed air of the stream a is compressed in the main air compressor 2 to a pressure of approximately 5 to 7 bar, for example. A correspondingly compressed stream, now designated b, is fed to a cooler unit 3 operated by cooling water streams that are not shown separately, where the previously fed heat of compression is withdrawn from the stream b. A correspondingly cooled stream, now designated c, is freed from the predominant part of the water and carbon dioxide present in an adsorptive purification unit 4 which can comprise, for example, a pair of adsorber containers filled with molecular sieve that are not shown separately. A stream purified in this manner, now designated d, is fed to a booster 5 and boosted therein to a pressure of, for example, approximately 9 bar. A correspondingly boosted stream, now designated e, is fed into a heat-exchange system of the air treatment unit, which is here designated overall 10.

In the heat-exchange system 10 of the air treatment unit 110, the compressed feed air of the stream e is cooled in a first heat-exchange unit 11 against a stream f of a heat-transfer fluid, obtaining a corresponding cooled stream g. The stream f and the stream e are in this case each at pressure levels which are above and hereinafter designated as “first” pressure levels. The stream f is brought by means of a pump 15 explained hereinafter to its “first” pressure level, the stream g by means of the compression explained. Values for the “first” pressure levels and possible deviations of these from one another have already been explained. The cooled stream g, in the example shown, is expanded in a generator turbine 12 and optionally an expansion valve which downstream thereof and is not shown separately. The correspondingly expanded stream g is transferred to a separation container 13, a liquid fraction forms in the sump thereof and at the top of which a gaseous fraction forms. The liquid fraction from the sump of the separation container 13 is transferred in the form of the stream h to a storage system 20, in which it is stored in the first operating mode. The storage system 20, can in addition to the stream h, as already mentioned above, also be charged with further liquid low-temperature streams. In the first operating mode, in the example shown no fluid is withdrawn from the storage system 20.

The gaseous fraction from the top of the separation container 13 is withdrawn in the form of the stream i and warmed in a further heat-exchange unit 14, which here is designated a fourth heat-exchange unit 14, as compared with the second and third heat-exchange units 16 and 18 explained hereinafter. In the fourth heat-exchange unit 14, in this case, cold can be transferred from the stream i to a stream k, which likewise comprises a heat-transfer fluid and is combined with a further corresponding stream l to form the abovementioned stream f of the heat-transfer fluid. The stream f and the streams k and l form two subcircuits of a heat-transfer fluid that are driven by means of the pump 15 and, therein and also in the first heat-exchange unit 11, are linked to one another. It is stressed, as already above, that in the subcircuits mentioned, no cold-producing expansion of a corresponding heat-transfer fluid proceeds, this serves substantially only for transferring heat, but not for the generation thereof.

The stream l, upstream of the combination to give the stream f and the feed into the heat exchanger 11 by means of the pump 15, or, after division of the stream f into the streams k and l downstream of the heat-exchange unit 11, i.e. at the warm end thereof, is conducted through the abovementioned two further heat-exchange units 16 and 18, namely the second heat-exchange unit 16 and the third heat-exchange unit 18, in which the stream l is cooled in each case by means of organic coolants which are respectively provided by coolant units 17 and 19. Details on the heat-exchange units 16 and 18 and also on the coolant units 17 and 19 are explained with reference to FIGS. 2A and 2B, and also 3A and 3B.

For provision of further cold from the compressed feed air of the stream d, a substream m can be branched off, cooled in the heat exchanger 14 to an intermediate temperature cold-producingly expanded in a generator turbine that is not shown separately and recirculated through the heat exchanger 14. A correspondingly recirculated stream can be used, for example, in the form of the stream n as regeneration gas in the adsorptive purification unit 4. The stream i can be combined with the stream d, for example upstream of the booster 5.

Further components of the air-treatment unit 110 and components of the energy generation unit 120, which is not in operation in the first operating mode shown in FIG. 1A will be described hereinafter with reference to FIG. 1B, in which the second operating mode is illustrated.

In FIG. 1B, the combined plant 100, which has already been illustrated in the first operating mode in FIG. 1A, is shown in the second operating mode. In the second operating mode illustrated in FIG. 1B, the stream e is not provided, the main compressor 2 and the booster 5 can be out of operation or be operated in a standby operation. The adsorptive purification appliance 4 can be regenerated, for example, during the second operating mode illustrated in FIG. 1B. Correspondingly, in the generator turbine 12 no cooled compressed feed air is expanded, and no fluid is transferred into the storage system 20 either. Also, the coolant circuit through the fourth heat-exchange unit 14 that is implemented in the first operating mode according to FIG. 1A by the stream k, is here typically not in operation.

Instead, in the second operating mode according to FIG. 1B, fluid is withdrawn from the storage system 20 in the form of the stream o, that is to say a stored liquid, and provided in the form of a low-temperature process liquid. In the first operating mode according to FIG. 1A, a low-temperature air liquefaction product is fed from the sump of the separation container 13 into the storage system. The stream o, in the second operating mode, is warmed in the heat exchanger 11 and vaporized. The stream o in this case transfers the cold thereof to a stream p which is formed from the same heat-transfer fluid of the streams f, k and l of the first operating mode according to FIG. 1A, but here, on account of clearer differentiability, is shown differently. The streams o and p are each at pressure levels which are designated above and hereinafter as “second” pressure levels. The stream o is brought to the “second” pressure level thereof by means of a pump that is not drawn separately, the stream p has this pressure level after it is conducted through the second heat-exchange unit 16 and the third heat-exchange unit 18 by means of the explained pump 15. Values of the “second” pressure levels and possible deviations thereof from one another have already been explained. A coolant circuit implemented in the second operating mode according to FIG. 1B by the stream p also comprises the abovementioned second and third heat-exchange units 16 and 18, and the associated coolant units 17 and 19, which are explained in the FIGS. 2A and 2B, and 3A and 3B, hereinafter.

A gaseous or supercritical pressurized fluid in the form of the stream q is provided by the warming and vaporization of the stream o, that is to say of the low-temperature process liquid, which stream q is fed to the energy generation unit 120. In the energy generation unit 120, the stream q is, for example, work-producingly expanded, with generation of electrical energy in a generator turbine 121. The stream q can be conducted in advance through a heat exchanger 122 and warmed therein by means of an exhaust gas stream of a combustion chamber 123 or a thermal engine, in which a fuel is burnt with air or another oxygen-containing gas.

In FIG. 2A, the second heat-exchange unit 16 with the associated coolant unit 17 of the plant 100, as shown in FIGS. 1A and 1B in the first and second operating modes, is illustrated in the first operating mode. The stream l of the heat-transfer fluid is conducted through the second heat-exchange unit 16, as already illustrated in FIG. 1A. A gaseous stream r is conducted in counterflow to the stream l, which stream r flows out of a first coolant store 171, is cooled in the second heat-exchange unit 16 and then flows into a second coolant store 172. The gaseous stream r is gas which does not condense at the above described temperatures, for example nitrogen. The stream r is provided by increasingly displacing corresponding gas from the first coolant store 171. For this purpose, an organic coolant is withdrawn in liquid form by means of a pump 173 from the second coolant store 172, conducted through the heat exchanger 16 and fed into the first coolant store 171. A corresponding stream of the organic coolant is designated s.

In FIG. 2B, the second heat-exchange unit 16 is shown in the second operating mode with the associated coolant unit 17, which is shown in FIG. 2A in the first operating mode. As already explained with reference to FIG. 1B, here a stream p of the heat transfer fluid is conducted through the second heat-exchange unit 16. An organic coolant or a gas overlaying it is conducted into the storage containers 171 and 172 in the second operating mode, which is shown in FIG. 2B, in reverse direction in comparison with the first operating mode which is shown in FIG. 2A. Corresponding streams are therefore illustrated with r′ and s′.

In FIGS. 3A and 3B, the third heat-exchange unit 18 with the associated coolant unit 19 of the plant 100 is illustrated in the first and second operating modes, which plant is shown in FIGS. 1A and 1B in the first and second operating modes. Two organic coolant streams which, for example, comprise propane as coolant, are used. The basic mode of functioning of the coolant unit 19 has already been explained with reference to FIGS. 2A and 2B. In the first operating mode, as is illustrated in FIG. 3A, in this case a first coolant stream t is conducted completely through the third heat-exchange unit 18, a second coolant stream u only through a section of this third heat-exchange unit 18. Corresponding coolant stores and pumps are here designated 191 to 196. Again the coolant streams which are conducted in reverse direction in the second operating mode which is illustrated in FIG. 2B are designated t′ and u′. The respective gaseous fluid streams likewise used are designated in the two FIGS. 2A and 2B with v and w, and v′ and w′, respectively. Coolants can also be exchanged between the two coolant circuits in the two modes of operation, as is illustrated by x and x′.

FIG. 4A illustrates a combined plant according to a further embodiment of the invention in the first operating mode in the form of a process flow diagram, where here only the heat-exchange system 10 is illustrated, the incorporation of which into the combined plant can be substantially the same as in the combined plant 100 according to the FIGS. 1A and 1B. Again, in FIG. 4A the first operating mode, and in FIG. 4B the second operating mode, of the combined plant is illustrated.

The boosted stream e is divided into two substreams according to FIG. 4A upstream or in the heat-exchange system 10 and is cooled in the first heat-exchange unit 11 and also in the fourth heat-exchange unit 14. In the first operating mode of the combined plant shown in FIG. 4A, however, only a stream f of a heat-transfer fluid is conducted through the first heat-exchange unit 11, a stream k, as is shown in FIG. 1A, therefore does not exist. The stream l corresponds according to FIG. 4A to the stream f. The cooled stream g is formed by combining the substreams of the stream e. The stream g, as already explained in FIG. 1A is vaporized and stored. The streams i and m have also already been explained above.

In FIG. 4B, the combined plant is shown in the second operating mode, which combined plant is illustrated in FIG. 4A in the first operating mode. For details not explained here, reference may be made to FIG. 1B. In the second operating mode illustrated in FIG. 4B, a substream of the liquefied air product or the stored liquid formed therefrom does not flow through the fourth heat-exchange unit 14. Only a stream 1 is conducted through the first heat-exchange unit 11, as already explained in FIG. 2B.

That explained several times above applies to the “first” pressure levels of the streams f and g and the “second” pressure levels of the streams o and p in FIGS. 4A and 4B.

In FIG. 5 a heat-exchange diagram achievable according to an embodiment of the invention is illustrated, and designated overall 500. In the diagram, an exchanged heat in kW is plotted on the abscissa and a temperature in K on the ordinate.

501 illustrates a heat-exchange profile for the compressed feed air, 502 a heat-exchange profile for the stored liquid formed from the liquefied air product, and 503 and 504 illustrate heat-exchange profiles for the heat-transfer fluid. It can be seen from the heat-exchange diagram 500 that the invention permits a particularly narrow guidance of the heat-exchange profiles 501 and 503, and 503 and 504, respectively. 

What we claim is:
 1. A process for storage and recovery of energy using a combined plant that comprises a gas treatment unit and an energy generation unit, wherein in a first operating mode, a low-temperature gas liquefaction product is generated from compressed feed gas that is cooled in a heat-exchange system of the gas treatment unit, and using the gas liquefaction product, a stored liquid is provided, in a second operating mode, using the stored liquid, a low-temperature process liquid is provided that is warmed in the heat-exchange system, obtaining a pressurized fluid that is work-producingly expanded in the energy generation unit, the compressed feed gas is cooled in a first heat-exchange unit of the heat-exchange system in the first operating mode in counterflow to a heat-transfer fluid, and the process liquid is warmed in the first heat-exchange unit in the second operating mode in counterflow to the heat-transfer fluid, the heat-transfer fluid is cooled in the first operating mode at least in part by means of at least two further heat-exchange units of the heat-exchange system that are operated at different temperature levels, and also each having at least one organic coolant, and said heat-transfer fluid is warmed in the second operating mode, the directions in which the heat-transfer fluid and the feed gas are conducted through the first heat-exchange unit in the first operating mode are opposite to the directions in which the heat-transfer fluid and the process liquid are conducted therethrough in the second operating mode, and the heat-transfer fluid and the compressed feed gas are conducted, in the first operating mode, in each case at first pressure levels, and the heat-transfer fluid and the process liquid, in the second operating mode, are conducted in each case at second pressure levels through the first heat-exchange unit, wherein the first pressure levels are at least 5 bar above the second pressure levels.
 2. The process according to claim 1, in which the heat-transfer fluid used is free from, or low in, oxidizing and combustible components.
 3. The process according to claim 1, in which the heat-transfer fluid used is a fluid predominantly containing nitrogen, neon, helium and/or argon.
 4. The process according to claim 1, in which an air treatment unit is used as gas treatment unit and in the first operating mode a low-temperature air liquefaction product is generated as gas liquefaction product from compressed feed air as compressed feed gas which is cooled in the heat-exchange system of the air treatment unit.
 5. The process according to any claim 1, in which the first pressure levels of the first operating mode are at 50 to 120 bar, and/or the second pressure levels of the second operating mode are at 40 to 60 bar.
 6. The process according to claim 1, in which the at least two further heat-exchange units comprise a second heat-exchange unit that is operated with a first organic coolant that is transferred between two storage containers.
 7. The process according to claim 6, in which the first organic coolant used is a fluid that contains a halogenated or non-halogenated alkane or alkene, at least one alcohol and/or at least one aromatic.
 8. The process according to claim 7, in which the at least two further heat-exchange units comprise a third heat-exchange unit that is operated with a second organic coolant that is transferred between two storage containers and that is further operated with a third organic coolant that is transferred between two storage containers.
 9. The process according to claim 8, in which the second organic coolant is warmed in the first operating mode from a first temperature level at −200 to −140° C. to a second temperature level at −100 to −30° C. and in the second operating mode is cooled from the second temperature level to the first temperature level.
 10. The process according to claim 9, in which the third organic coolant in the first operating mode is warmed from a third temperature level at −200 to −140° C. to a fourth temperature level at −140 to −60° C. and in the second operating mode is cooled from the fourth temperature level to the third temperature level.
 11. The process according to claim 10, in which, in the first operating mode, the second organic coolant at the first temperature level and the third organic coolant at the third temperature level are fed to the second heat-exchange unit, and the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level are withdrawn therefrom and/or in which, in the second operating mode, the second organic coolant at the second temperature level and the third organic coolant at the fourth temperature level are fed to the second heat-exchange unit, and the second organic coolant at the first temperature level and the third organic coolant at the third temperature level are withdrawn therefrom.
 12. The process according to claim 8, in which as the second coolant, and the third organic coolant, an identical fluid is used.
 13. The process according to claim 8, in which the second organic coolant and/or the third organic coolant a fluid is used that contains a halogenated or non-halogenated alkane or alkene having at most four carbon atoms.
 14. The process according to claim 1, in which a fourth heat-exchange unit is used, by means of which the heat-transfer fluid is in part cooled in the first operating mode and which is operated with a further compressed feed gas that is cold-producingly expanded.
 15. The process according to claim 9, in which the second organic coolant is warmed in the first operating mode from a first temperature level −196 to −150° C., to a second temperature level at −60 to −40° C., and in the second operating mode is cooled from the second temperature level to the first temperature level.
 16. The process according to claim 10, in which the third organic coolant in the first operating mode is warmed from a third temperature level at −196 to −150° C. to a fourth temperature level at −100 to −60° C., and in the second operating mode is cooled from the fourth temperature level to the third temperature level.
 17. A combined plant for storage and recovery of energy, having a gas treatment unit and an energy generation unit, wherein the combined plant has means which are equipped to generate a low-temperature gas liquefaction product, in a first operating mode, from compressed feed gas that is cooled in a heat-exchange system of the gas treatment unit, and using the gas liquefaction product, to provide a stored liquid, to provide a low-temperature process liquid, using the stored liquid, in a second operating mode, to warm said low-temperature process liquid in the heat-exchange system, obtaining a pressurized fluid, and to work-producingly expand the pressurized fluid in the energy generation unit, to cool the compressed feed gas in a first heat-exchange unit of the heat-exchange system in the first operating mode in counterflow to a heat-transfer fluid, and to warm the process liquid in the first heat-exchange unit in the second operating mode in counterflow to the heat-transfer fluid, to cool the heat-transfer fluid in the first operating mode at least in part by means of at least two further heat-exchange units of the heat-exchange system that are operated at different temperatures and also with respectively at least one organic coolant, and to warm said heat-transfer fluid in the second operating mode, to set the directions in which the heat-transfer fluid and the feed gas are conducted through the first heat-exchange unit in the first operating mode opposite to the directions in which the heat-transfer fluid and the process liquid are conducted therethrough in the second operating mode, and to conduct the heat-transfer fluid and the compressed feed gas, in the first operating mode, in each case at first pressure levels, and the heat-transfer fluid and the process liquid, in the second operating mode, in each case at second pressure levels through the first heat-exchange unit, wherein the first pressure levels are at least 5 bar above the second pressure levels. 